1. Field of the Invention
The present invention relates to a semiconductor photocathode which generates an electron in response to light incident and accelerates and emits thus generated electron with an externally applied voltage, as well as a semiconductor photocathode apparatus using the same.
2. Related Background Art
T.E. photocathode (transferred electron semiconductor photocathode) disclosed in U.S. Pat. No. 3,958,143 is known as an example of photocathodes which forms an electric field with an external applied bias voltage, transfers a photoelectron to its emission surface, and then emits the photoelectron. The operation mechanism of T.E. photocathode is disclosed in several publications. In brief, a Schottky electrode is formed on the whole surface of a III-V semiconductor (p.sup.-), and a positive potential is given thereto. Consequently, a gradient electric field is formed within the photocathode, so as to accelerate the photoelectron generated in response to light incident. Thus, the energy level of the photoelectron shifts to an upper conduction band, thereby exceeding the energy barrier of the photocathode surface so as to be emitted into the vacuum. It has been confirmed that the T.E. photocathode can effectively respond to light having a wavelength as short as 2.1 .mu.m. Also, in this semiconductor photocathode, the efficiency of photoelectric conversion can be improved when the Schottky electrode is formed like a grid.
On the other hand, U.S. Pat. No. 5,047,821 and Japanese Patent Application Laid-Open No. 4-269419 disclose techniques for constantly making semiconductor photocathodes with a favorable reproducibility.
The quantum efficiency of these semiconductor photocathodes is about 0.1%, which is lower than that of typical photodetectors. In order to be used as a practical photodetector, it is desirable for the semiconductor photocathode to have a higher quantum efficiency. Such a low quantum efficiency is supposed to be due to the fact that photoelectrons are captured with a low efficiency by the Schottky electrode formed on the surface.
In view of the foregoing problems, it is an object of the present invention to provide a semiconductor photocathode which can further improve the quantum efficiency.
It is another object of the present invention to provide a semiconductor photocathode apparatus using such a semiconductor photocathode.